Approximately 80% of the global energy demand comes from fossil fuels, including coal, petroleum, and natural gas, and this reliance on fossil fuels is expected to increase. The combustion of fossil fuels produces CO2, which may continue to effect climate change. As a result, a number of strategies are being explored to efficiently separate and store CO2 in large stationary sources, such as fossil fuel based power plants, which produce over 50% of the electricity in the U.S., rather than in mobile platforms, i.e. automobiles. For example, coal can be gasified to produce synthesis gas containing mostly carbon monoxide, steam, O2, N2 and hydrogen. This synthesis gas can be sent to a water gas shift (WGS) reactor to convert carbon monoxide and steam to carbon dioxide and hydrogen. The hydrogen can then be separated using a hydrogen separation membrane, leaving the non-permeating CO2 product at pressure or using the hydrogen and CO2 for other processes. The hydrogen separation technique could be applied to many other processes including steam reformed natural gas, ammonia purge gas streams, methanol or other fuels and chemicals from synthesis gas, refinery off-gas streams, and fuel-cell power systems for transportation.
Global production of H2 stands at about 50 million tons/year, and is increasing due to continued expansion of hydrocracking operations required by low grade fuels such as tar sands. Over 95% of H2 is derived from fossil fuels such as natural gas or coal through processes such as steam reforming that yield the following overall reactions:CH4+2H2O→4H2+CO2  (1)C(s)+2H2O→2H2+CO2  (2)These processes proceed through CO as an intermediate, and overall conversion is limited by the equilibrium nature of the WGS reaction:H2O+CO⇄H2+CO2  (3)
High temperature, inorganic membrane technology is currently being investigated to perform many of the separations needed for co-generation of electric power or hydrogen from fossil fuels while simultaneously concentrating and capturing CO2. However, the current lack of economical separation technology for these high temperature applications makes H2 recovery unfeasible.
A method for making perfectly selective metallic membranes that are permeable to hydrogen using a palladium catalyst layer on both sides of a hydrogen permeable metal or metal alloy substrate from Group VI and Group V of the Periodic Table including vanadium, niobium and tantalum, is generally known in the art. The palladium catalyst layer allows Group VI and Group V metal membranes to be used as hydrogen separation membranes. However, at temperatures above 350° C., the palladium catalyst layer diffuses into the metal membrane and the hydrogen permeability performance decreases dramatically. Furthermore, there is a high cost associated with applying and using the palladium and palladium alloy catalysts.
Thus, there is a significant need in the energy industry and other related fields to provide an economical membrane that is permeable to hydrogen over a broad temperature range and process to purify hydrogen from contaminants as well as other compounds.